Perhaps no other subject pertaining to adverse impacts on wildlife by human activity has generated more global concern and response during the past decade than the well-documented occurrences of poisoning in a wide variety of avian (and other) species by incidental ingestion of lead (Pb), almost entirely attributed to spent ammunition. For example, approximately 150 professional bioscientists from throughout the USA, Canada, Europe, Australia, et al. met during May 12-15, 2008 in Boise, Id. at a conference sponsored by The Peregrine Fund, United States Geological Survey, Tufts Center for Conservation Medicine and Boise State University, and entitled, “Ingestion of Lead from Spent Ammunition: Implications for Wildlife and Humans.”
While no attempt will be made herein to discuss the 53 invited technical presentations at the Boise conference, it is relevant to offer brief examples of general consensus among the participants:
(1) Outlawing of lead shot for hunting waterfowl in the U.S. and Canada has drastically reduced losses of ducks, geese, et al. by lead poisoning and has not contributed to other types of loss (for example, by crippling due to steel shot). Serious consideration is being given throughout the U.S. to extending the ban on lead shotgun shot to other types of bird and small-game hunting. While steel shot is considered to be acceptable for its intended purpose, it should be noted that it is only considered to be appropriate for modern shotguns with relatively hard steel barrels. It is therefore not recommended for a wide spectrum of older, fine-quality guns manufactured prior to the modern prohibitions against toxic lead shot. This factor is quite relevant to some embodiments of the present disclosure.
(2) Voluntary restriction of the use of lead bullets for big-game hunting was not sufficiently effective in the condor range of California, but produced somewhat better results in Arizona and Utah. Both scavengers and raptors eat carrion, such as that associated with lead-killed animals.
(3) California will continue to enforce its July 2008 mandatory statewide ban on lead bullets (including not only “centerfire” big-game and varmint bullets, but also smaller “rimfire” bullets for target and varmint shooting).
(4) Other U.S. states and many foreign countries are presently in various stages of studying further lead bullet restrictions, and some countries have already instituted new policies and/or laws.
(5) While as yet unproven, there is evidence that game meat contaminated with small lead fragments may constitute an unnecessary risk to humans who knowingly or innocently ingest them. This concern, whether fully justified or not, has resulted in warnings to the public by governmental health agencies and in curtailment of distribution of game meat to charitable agencies and organizations.
At the present time, bullets comprised primarily of copper (Cu) and copper alloys (e.g., Cu—Zn and Cu—Sn) are the most popular available alternatives to lead. Barnes Bullet Company pioneered a wide spectrum of pure copper bullets, beginning as far back as 1985, as represented in U.S. Pat. No. 5,131,123, the disclosure of which is hereby incorporated by reference. It is relevant to note that the incentive for these efforts was based upon claimed superior bullet ballistic performance, rather than on any consideration of toxicity. Since the California ban, several other manufacturers have offered other types of copper-based bullets, all of which, as already mentioned, contain copper as the primary constituent.
While an interim consensus was evident at the Boise conference that copper was much preferable to lead, actual in vivo tests of American kestrels (the target/study bird selected as representative of raptors and scavengers), in which subject birds have been gavaged (i.e., force-fed) with solid copper samples, are scheduled to be completed sometime during the spring of 2011 by USGS personnel. It should be noted that bullets produced from both solid and particulate forms of copper and its alloys are presently being offered by manufacturers, the different varieties of which may have correspondingly different dissolution rates, toxicities, etc. when ingested by birds or other living creatures.
Aside from toxicological considerations, intensive debate continues among sportsmen and wildlife personnel as to the impact of additional costs associated with non-toxic, copper-based ammunition, especially in such areas as varmint and/or target shooting, sports in which relatively large numbers of cartridges are expended. Copper bullets typically cost several times as much as traditional copper-jacketed lead bullets, a factor which is perceived as potentially reducing the number of hunters/shooters, as well as the frequency of their activities. From a conservationist standpoint, hunters who are reluctant or unable to practice their skills are more likely to wound game animals, with resulting waste of the resource.
The dual requirements of non-toxicity and economy argue for development of projectiles made, in whole or in part, from steels. Common grades of steel (for example, in wire/rod form) are available at commodity prices (per unit weight) that are approximately 60% of those of lead and only about 15% of those of copper. Considerations of acute and low-level/long-term toxicity and “environmental fate” also demonstrate attractive attributes of iron and steel. Iron (Fe), the fourth most abundant element on earth, is generally considered to be “environmentally friendly” and easily oxidized to insoluble compounds. No other metallic material can begin to compare with steel from the standpoints of industrial experience, metallurgical technology, product diversity, variety of available process capability, etc. While steel bullet and jacket types have been used in certain military applications (often motivated by war-time shortages of critical materials such as copper and lead), one might well ask why steel bullets have not been applied to a wider variety of bullets, including those suitable for law enforcement and civilian applications.
Whereas military bullets for such common calibers as 0.223 in. (5.56 mm) and 0.30 in. (7.62 mm) are prohibited from expanding (“mushrooming”) or fragmenting by international agreements (e.g., The Hague and Geneva Conventions), bullets used for big-game, small-game, and varmint hunting are designed specifically to expand and/or fragment in the target. An exception to this is found in very large African game, for example, elephant or cape buffalo, for which solid brass or other alloy bullets are designed to penetrate heavy skulls. A further consideration in hunting bullets is that they are preferably designed to penetrate and expand in a controlled manner, often specific to particular sizes and/or species of animals. A primary objective is for the bullet to penetrate sufficiently to reach critical organs, while depositing all or most of its energy in vital regions. Premature expansion may result in non-lethal “flesh wounding,” while delayed expansion may allow the bullet to pass entirely through the animal, leaving an under-sized wound path and wasting kinetic energy beyond the target.
In law enforcement applications for bullets, penetration and expansion also are important attributes to be controlled. As in hunting applications, it may be desirable for a bullet to expand in such a manner as to deposit all of its kinetic energy in the target, in this case, a human being deemed to be a threat to the lives of peace officers or others. However, the human factor greatly complicates bullet requirements for given situations. For example, a perpetrator may be wearing a variety of clothing (including body armor), which significantly affects bullet expansion and subsequent penetration. This variable is especially important when “hollow point” bullets are employed, since different types of cloth may plug the bullet's nose cavity, thereby preventing it from expanding properly. Police officers also face many situations in which the perpetrator is shielded behind barriers such as automobile windshields, construction materials, panels, etc., situations which could benefit from a highly penetrative bullet. Further complicating the law officer's responsibilities are considerations of bullet over-penetration and ricocheting, both of which may result in injury to bystanders. Because of these and other factors, law enforcement agencies must constantly make potentially “life and death” decisions as to precisely which bullet types represent the best compromise for officers to carry at a particular instance.
Both accuracy and retained energy of bullets are influenced by such factors as bullet density (mass-per-unit-volume), dimensions and shape, as well as variables inherent in gun barrel design (e.g., length, twist rate, etc.) and environment (e.g., air temperature, pressure, humidity, etc.). While bullet density may be directly related to energy retention and fluid drag resistance, the success attained with solid copper bullets (e.g., Barnes Bullets, Inc. products) during the past 25 years illustrates that lower material density need not be viewed as an insurmountable obstacle to acceptable ballistic performance. In fact, several advantages of such bullets have been claimed, including that lighter bullets may be launched at higher velocities (for a given barrel pressure) and therefore may actually display less gravitational drop at certain distances. Another factor is that copper bullets “mushroom” in a manner quite different from conventional lead hunting bullets. In the former, the unfolded bullet “petals” created at impact remain attached to the base of the bullet (thereby retaining integral mass), while lead bullets tend to shed and scatter fragments of lead along the wound path (poor “weight retention”). This characteristic behavior observed in many lead bullets is presumably the result of its extreme softness and low melting point.
Because expanding copper bullets (8.96 g/cc density) perform well enough to satisfactorily substitute for corresponding lead bullets (11 glee density), obtaining acceptable performance with steel bullets also appears to be feasible. The shift in density from lead to copper represents a decrease of about 22%, whereas the difference between steel at 7.86 glee and copper is only about 14%. Appropriate grades of low-carbon steel, properly fabricated in accordance with specific processes and bullet designs, possess sufficient ductility to replicate the “folded petal” behavior of copper, including its inherently high weight-retention, when desired.
Another factor, which cannot be ignored, is that a bullet must possess surface properties such that the machined rifling grooves in modern gun barrels are not prematurely eroded, nor are they filled or “fouled” by bullet residues. With lead-core bullets, fouling is prevented by individually encapsulating cores in copper alloy (often 97% Cu-5% Zn “gilding metal”) jackets. These jackets typically are separately formed “housings” into which the bullet core is positioned during production of the assembled bullet. The jacket also contributes significantly to the overall strength of the bullet, which must withstand high rotational and translational stresses without flying apart or “obturating” (i.e., becoming mechanically distorted) in flight. In addition to encapsulating the main bearing surface of the bullet in this way, it is usually necessary to place a “gas check” disc on its rearward face to prevent the melting of lead by hot combustion gases upon firing the cartridge. Other means of coating conventional lead-cored bullets include electrolytic plating (restricted to cartridges with relatively low velocities), non-metallic coatings (e.g., nylon,), and jacketing sub-sized bullets in relatively thick plastic “sabots.” Obviously, none of these bullet coating schemes is necessary in the case of solid copper bullets.
While an inexperienced engineer or metallurgist might assume that a metallic shape of basically round cross-section (e.g., a bullet) could be advantageously clad in a different metal by means of a continuous process, resulting in a long clad wire, attempts to do so with lead and copper have proven to be technically and economically impractical. This is believed to be primarily due to the widely different mechanical, physical and metallurgical properties of such dissimilar metals as lead and copper. The overall result of these property differences is that conventional high-velocity bullets must be produced by individually fitting each lead core with a precisely-tailored copper alloy jacket, and then maintaining precision, uniformity, repeatability, etc. throughout all subsequent operations. While many bullet manufacturers make advertising claims of “bonded” bullets, consideration of the Cu—Pb equilibrium diagram illustrates that there is no discernable solid solubility (i.e., “alloying”) directly between solid copper and solid lead, indicating that any so-called “bonding” would be metallurgically marginal. Conversely, the Cu—Fe binary system does, in fact, display significant degrees of solid solubility, both in Cu-rich and Fe-rich regions of the alloy system.
Bonding strength between jackets and cores is not a trivial consideration, with respect to both performance and safety. For example, if jacket material is “stripped” from the core as the bullet travels down the gunbarrel, it may become lodged in the barrel, resulting in an obstruction to subsequent firings. Conventional swaged jacket-core assemblies must be held to strict production quality-control standards to ensure adequate bond strengths. Electroplated copper jackets are viewed as having relatively low bonding strengths to degrees that limit their usefulness to low velocities (e.g., in pistols and a few relatively low-power rifles).
In the case of steel shotgun pellets, copper, zinc, and nickel are routinely applied as electroplated films by various manufacturers to obtain some degree of corrosion-resistance, along with aesthetically pleasing surface appearance. These films, however, are relatively thin (e.g., 0.0005-0.001 inch), porous, and merely mechanically bonded to steel substrates. None of these coated steel pellet types is considered to be acceptable for use in older shotguns, the present markets being served by expensive alternatives to lead, such as bismuth.